An AC surface discharge panel as a representative example of plasma display panel (or panel) is formed of multiple discharge cells provided between front substrate and rear substrate disposed oppositely.
On the front substrate, a display electrode pair composed of scan electrode and sustain electrode is formed in a plurality of pairs mutually parallel on the front glass substrate, and on the rear substrate, a plurality of data electrodes are formed parallel on the rear glass substrate. The front substrate and the rear substrate are disposed oppositely and sealed so that the display electrode pair and the data electrode may intersect, and the internal discharge space is packed with discharge gas. Discharge cells are formed in the confronting portions of the display electrode pair and the data electrode.
As a method of driving a panel, generally, a so-called subfield method is used, that is, one field period is divided into a plurality of subfields, and the gradation is displayed by combination of subfields for emitting light. Each subfield has an initializing period, an address period, and a sustain period. In the initializing period, initializing discharge is generated, and a wall charge necessary for subsequent address operation is formed on each electrode. In the address period, a scan pulse is sequentially applied to each scan electrode, and an address pulse is applied selectively to the data electrode of the discharge cell for display, and address discharge is generated. In the sustain period, sustain pulses are alternately applied to a display electrode pair, and sustain discharge is generated in the discharge cell causing address discharge to emit light, and thereby an image is displayed.
The subfield method includes various driving methods deviated in the timing of generation of address discharge in individual scan electrode groups by dividing the scan electrode into a plurality of scan electrode groups. For example, patent document 1 discloses a driving method in which relatively lower voltages are applied to second scan electrode groups as second voltages, while scan pulses are applied to first san electrode groups, and then set-down pulses to fall gradually to third voltages are applied. However, while scan pulses are applied to one scan electrode group, when lower voltages are applied to other scan electrode groups, the wall charge required for the address operation is decreased in the scan electrode groups provided with lower voltages, and normal address discharge may not be generated.
However, when driving the panel by using the subfield method, only by applying address pulses to data electrodes, if scan pulses are not applied to scan electrodes, the wall charge required for the address operation may be decreased, and normal address discharge may not be generated. To solve this problem, for example, patent document 2 discloses a driving method in which the scan electrode is divided into four scan electrode groups, the address period is divided into four periods for applying scan pulses sequentially to the scan electrodes belonging to each scan electrode group, and higher voltages are applied to the scan electrode groups not provided with scan pulses than in the scan electrode groups provided with scan pulses.
In this driving method, however, the voltage difference of adjacent scan electrodes may be excessive at a certain timing, and sparks may be generated between panel electrode terminals or wiring patterns of printed wiring board. There is also possibility of occurrence of shorting in the scan electrode drawing-out portions of the panel due to migration. Besides, since a driving voltage is applied from the scan electrode driving circuits corresponding to the individual scan electrode groups, a slight difference may be caused in the driving voltage waveform in every scan electrode group, and a contour may be formed in the image display region corresponding to the boundary of the scan electrode groups, which may lead to lowering of image display quality.    [Patent document 1] Japanese Unexamined Patent Publication No. 2007-65671    [Patent document 2] Japanese Unexamined Patent Publication No. 2003-43989